Update README.md

README.md

 # Official Jenkins Docker image
 
+# Approved for use behind a CNAP/CPN. It cannot be internet facing.
+
 [![Docker Stars](https://img.shields.io/docker/stars/jenkins/jenkins.svg)](https://hub.docker.com/r/jenkins/jenkins/)
 [![Docker Pulls](https://img.shields.io/docker/pulls/jenkins/jenkins.svg)](https://hub.docker.com/r/jenkins/jenkins/)
 [![Join the chat at https://gitter.im/jenkinsci/docker](https://badges.gitter.im/jenkinsci/docker.svg)](https://gitter.im/jenkinsci/docker?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)